1. Field:
The subject apparatus is in the field of water sports equipment, more specifically equipment which enables the user to be supported in an erect postion and self-propelled on water or land. More specifically, it is in the field of such equipment comprising a pair of elongated floats adapted to fit on the feet of the user with propulsion accomplished by walking or striding motion.
2. Prior Art:
There is profuse prior art for this invention, even in the specific field, some of the most pertinent described in U.S. Pat. Nos.: 3,601,828, 3,716,881, 3,758,898, 3,777,324, 4,037,280, and French Pat. No. 78 09169 and German Pat. No. 3342365.
It is clear from the prior art that there is a longstanding desire, if not need, for the subject type of apparatus. It is also clear that none of the prior art has achieved significant commercial success. It is believed that the lack of commercial success can be attributed to two significant factors, among others. First, the propulsion efficiency has been such that considerable endurance and athletic ability have been required to achieve satisfactory performance. Second, the various apparatuses have been subject to damage during ordinary usage, particularly the propulsion apparatus.
In regard to propulsion efficiency, propulsion on water is provided by flaps arranged such that when a float is moved forward, the flaps hinged to it fold against a surface parallel to the direction of motion and resistance to motion forward is reduced. When the float is moved in the aft direction, the flaps hinge outward to engage a volume of water and the acceleration of this water in the aft direction provides the desired propulsion force. For good efficiency, the flaps should hinge outward (fold open) in response to as little aftwise float motion as possible to engage the volume of water. Any aft motion before the flaps open and during the opening is lost motion, resulting in lower propulsion efficiency.
Also, the flaps should be fully submerged, regardless of the weight of the user and the corresponding amount of submersion of the floats to support the weight. Further, the flap working area should be as large as practical.
In the prior art apparatuses, some use propulsion flaps or equivalent on the sides of the floats. These flaps are not fully submerged. On some apparatuses the flaps are hinged to the bottoms of the floats. However, if flap area is approximately equal to the crossectional area of a float (i.e. each flap is square and as wide as a float), the lost motion to open the flaps is excessive. To explain, with the dimension of the flap edge hinged to the float denoted as the span, the dimension of the flap from the hinged edge to the opposite edge denoted as the chord and the flap square as described, the chord equals the span. The aft motion required to open the flap is approximately equal to the chord since the edge away from the hinged edge must move from essentially directly aft of the hinged edge to essentially directly below it. With the span equal to the chord, the lost motion is about equal to the width of the float and experience has shown that to be excessive.
Further, flaps mounted on the float bottom are fulnerable to damage if and when submerged objects are encountered or there is insufficient water depth for the necessary flotation.
In view of the above, it can be understood that a first objective of the subject invention is provision of propulsion apparatus having effective flap areas as large as 80% of the float crossectional area but with lost motion required to open the flap considerably less than the effective span. A second objective is that the propulsion flaps be mounted below the floats so that they are always fully submerged regardless of the weight of the user. A third objective is that the flaps not be vulnerable to damage from submerged objects and from use in shallow water or on land or other walk-on surfaces.